The aim of this project is to study mechanisms of immunity and immune evasion in schistosomiasis with the ultimate goal of developing an experimental vaccine employing defined antigens. A. Isolation of a protective vaccine antigen. Monoclonal antibodies were raised against a 97 kD protein recognized monospecificallly by mice vaccinated intradermally with schistosome extracts plus BCG. These monoclonals were used to purify the antigen which in preliminary experiments was shown to selectively elicit cell-mediated immunity (DTH, lymphokine production) in mice vaccinated with crude extracts. The anatomical localization and epitopic structure of the molecule were characterized and cellular and humoral responses to the antigen studied in infected or vaccinated mice as well as infected Kenyan and Brazilian patients. B. Studies on the immune dependence of praziquantel therapy. Through the use of Mu-suppressed mice, the major anti-schistosomal drug praziquantel was shown to be dependent on the host humoral response in its in vivo effect on adult worms.